The present invention relates to magnetic tape cassettes, and more particularly to a compact cassette used for audio use which is provided with an improved shield member.
Recently, cassette tape recorders have been remarkably reduced in both size and weight. In this connection, there has been a strong demand for provision of magnetic tape cassettes of small size and high quality which are suitable for high-density signal recording and reproducing operations. In order to meet this requirement, various magnetic tape cassettes, and also magnetic heads, have been proposed. In the design of the magnetic tape cassette, an important consideration is how to block stray external magnetic fields (hereinafter referred to merely as "noise" when applicable) during signal recording and reproducing, which is essential for maintaining good recording and reproducing characteristics.
For the above-described purpose, in a conventional magnetic tape cassette, as shown in FIG. 1, a shield plate 1 which is U shaped in cross section is provided in the opening 2 into which a recording and reproducing head 3 is inserted for recording and reproducing. A pair of head pins 4 are provided on a base 5 in the opening 2 on opposite sides of the magnetic head 3. A leaf spring 7 with a pressure pad is mounted on the base 5. The shield plate 1 is fitted in the cassette half in such a manner as to hold the leaf spring 7 from behind, and is itself held by the upper and lower cassette halves. A partition 8 is formed behind the shield plate 1 to separate the tape accommodating region and the recording and reproducing region from each other.
The shield plate prevents the magnetic head 3 from picking up external noise during a recording or reproducing operation. It is well known in the art that the shielding effect of the shield plate thus constructed can be improved by forming it of a material providing a higher shielding effect, by designing the shield plate so as to cover more of the magnetic head, or by disposing the shield plate closer to the magnetic head 3.
If the first method is employed, the manufacturing cost of the shield plate 1 is increased. Also, it is difficult to cover more of the magnetic head with the shield plate because of the dimensional standards of the cassette. With the structure of the opening 2 as described above, it is considerably difficult to set the shield plate 1 closer to the magnetic head 3 because of the dimensions of the shield plate and the dimensions of the magnetic head. In other words, since the shield plate 1 and the leaf spring 7 are small components and are arranged in engagement with each other, and since the shield plate 1 is held by the upper and lower cassette halves, it becomes more difficult to mount the shield plate 1. If the width of both end pieces 9 of the shield plate 1 is made smaller so that the shield plate 1 can be set closer to the magnetic head 3, then the assembly of the cassette becomes more difficult and there is a greater likelihood that the components will be assembled unsatisfactorily. When the magnetic head is mechanically inserted into the cassette, it tends to undergo an overdamped movement until it is held stably. Therefore, if the shield plate is closer to the magnetic head, then the latter may contact the former.